VDC horizontal display greater than 82.

willymanilly
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VDC horizontal display greater than 82. Oct 6, 2018 0:34:01 GMT

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Post by willymanilly on Oct 6, 2018 0:34:01 GMT

Hi all,

Has anyone had any success in displaying more than 82 non repeating characters on a single line?

When horizontal display (VDC register 1) is greater than 82, the characters at horizontal position 82 and higher seems to repeat starting at character position 42. See examples below.

For the tests I just used sys dec("cdcc"),hd,1 and then just readjusted the position of the test string so the first '1' is in the first column of the screen. The following results show only the first line of output. The + at the top of each result shows the column where the characters are replaced. The - shows which characters are used for the replacement.

The test string is "12345678901234567890123456789012345678901234567890123456789012345678901234567890ABCDEFGHIJ"

Changing the total horizontal positions, having attributes on or off, or changing the number of DRAM refresh cycles doesn't seem to affect these results.

I'd be very interested to get my hands on any examples where more than 82 horizontally displayed characters are used on the VDC.

reference:
                   1         2         3         4 repeat  5         6         7         8  MAX (replace chars from position 42 onwards with these when HD>82)
          12345678901234567890123456789012345678901234567890123456789012345678901234567890ABCDEFGHIJ

Horizontal Displayed=80 (Default Screen - obviously will display as expected)
sys dec("cdcc"),80,1
expected: 12345678901234567890123456789012345678901234567890123456789012345678901234567890
actual  : 12345678901234567890123456789012345678901234567890123456789012345678901234567890

Horizontal Displayed=82 (Matches)
sys dec("cdcc"),82,1
expected: 12345678901234567890123456789012345678901234567890123456789012345678901234567890AB
actual  : 12345678901234567890123456789012345678901234567890123456789012345678901234567890AB

Horizontal Displayed=83
sys dec("cdcc"),83,1                               +                                        -
expected: 12345678901234567890123456789012345678901234567890123456789012345678901234567890ABC
actual  : 12345678901234567890123456789012345678901C34567890123456789012345678901234567890ABC

Horizontal Displayed=85
sys dec("cdcc"),85,1                               +++                                      ---
expected: 12345678901234567890123456789012345678901234567890123456789012345678901234567890ABCDE
actual  : 12345678901234567890123456789012345678901CDE567890123456789012345678901234567890ABCDE

Horizontal Displayed=88
sys dec("cdcc"),88,1                               ++++++                                   ------
expected: 12345678901234567890123456789012345678901234567890123456789012345678901234567890ABCDEFGH
actual  : 12345678901234567890123456789012345678901CDEFGH890123456789012345678901234567890ABCDEFGH

Horizontal Displayed=90
sys dec("cdcc"),90,1                               ++++++++                                 -------- 
expected: 12345678901234567890123456789012345678901234567890123456789012345678901234567890ABCDEFGHIJ
actual  : 12345678901234567890123456789012345678901CDEFGHIJ0123456789012345678901234567890ABCDEFGHIJ

Last Edit: Oct 6, 2018 7:15:26 GMT by willymanilly

bjonte Plus/4 User Posts: 412	VDC horizontal display greater than 82. Oct 6, 2018 4:31:44 GMT via Tapatalk Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by bjonte on Oct 6, 2018 4:31:44 GMT This was unexpected.

bjonte Plus/4 User Posts: 412	VDC horizontal display greater than 82. Oct 6, 2018 7:37:19 GMT via Tapatalk willymanilly likes this Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by bjonte on Oct 6, 2018 7:37:19 GMT I get the same result on my test setup.

remark PET User Posts: 69	VDC horizontal display greater than 82. Oct 6, 2018 11:44:09 GMT Quote Select Post Deselect Post Link to Post Member Give Gift Back to Top Post by remark on Oct 6, 2018 11:44:09 GMT Don't you not also need to set R27 Adress increment per row to let the vdc know it needs to read 81+ consecutive ram locations instead of 80?
	it's more fun to compute

willymanilly
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Posts: 219

VDC horizontal display greater than 82. Oct 6, 2018 14:23:01 GMT

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Post by willymanilly on Oct 6, 2018 14:23:01 GMT

Oct 6, 2018 11:44:09 GMT remark said:

Don't you not also need to set R27 Adress increment per row to let the vdc know it needs to read 81+ consecutive ram locations instead of 80?

No, register 27 is used to set up a virtual screen wider than the visible part of the screen by telling the VDC how many memory locations (columns) to skip per row after the visible part. This makes it easier for scrolling the entire screen horizontally. The system default value for this register is 0.

tokra
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Posts: 185

VDC horizontal display greater than 82. Oct 6, 2018 16:09:16 GMT willymanilly likes this

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Post by tokra on Oct 6, 2018 16:09:16 GMT

Never managed to get more than 82 chars horizontally as well, no matter what I tried. The same barrier seems to apply for using color in hires-mode. While you can use monochrome modes like 800x600, with color horizontally I could never go over 656 (= 82 x 8) if I remember correctly.

willymanilly
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Posts: 219

VDC horizontal display greater than 82. Oct 7, 2018 1:10:29 GMT

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Post by willymanilly on Oct 7, 2018 1:10:29 GMT

Oct 6, 2018 16:09:16 GMT tokra said:

Never managed to get more than 82 chars horizontally as well, no matter what I tried. The same barrier seems to apply for using color in hires-mode. While you can use monochrome modes like 800x600, with color horizontally I could never go over 656 (= 82 x 8) if I remember correctly.

In light of all this I'm assuming the VDC only has 2 x 82 byte wide buffers for the character pointers and attributes. Monochrome bitmap doesn't require any of those buffers so shouldn't be restricted in horizontal pixel size as demonstrated by your monochrome interlaced images in VDC mode mania. I've actually discovered quite a few glitches and features I have not seen previously discussed.

for example, using the following command, if you put the cursor to the last visible line of the screen you will also see the cursor at the top of the screen. When you type you will only see characters appear at the bottom line of the screen.

sys dec("cdcc"),dec("4f"),24

Another example, if you scroll right down to the bottom of the screen, the cursor will appear at the top of the screen. If you start typing no characters will appear at the cursor position. If you scroll down one more line you will see the characters you just typed at the bottom of the screen.

sys dec("cdcc"),dec("58"),24

I have all the above modeled in the Z64K's new VDC emulation. I have also implemented much better status flag behaviour. I will release it later this month once I'm satisfied I haven't broken anything with the VDC emulation, especially to all the modes in VDC mode mania and VGA mode mania.

tokra
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Posts: 185

VDC horizontal display greater than 82. Oct 7, 2018 9:53:59 GMT

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Post by tokra on Oct 7, 2018 9:53:59 GMT

The buffer width of 82 would not explain why in 8x1-mode the width of the display can not go over about 60 chars (480 pixels). I think I got 61 or 62 chars width out of that, but after that the colors corrupt. Also I could never get 8x1-interlace-modes working.

I remember hydrophilic had an idea back in the old-forum-days, but sadly those posts are gone.

willymanilly
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Posts: 219

VDC horizontal display greater than 82. Oct 7, 2018 10:14:51 GMT

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Post by willymanilly on Oct 7, 2018 10:14:51 GMT

Oct 7, 2018 9:53:59 GMT tokra said:

The buffer width of 82 would not explain why in 8x1-mode the width of the display can not go over about 60 chars (480 pixels). I think I got 61 or 62 chars width out of that, but after that the colors corrupt. Also I could never get 8x1-interlace-modes working.

I remember hydrophilic had an idea back in the old-forum-days, but sadly those posts are gone.

Implementing the busy flag behavior has given some insight to why you had problems with extending your 8x1 mode. Basically you run out of VDC cycles to fetch the attribute data for each line.

The glitches you see in the text interlaced modes with attributes on with the following test program is because there are not enough VDC cycles to populate the buffers. sourceforge.net/p/vice-emu/code/HEAD/tree/testprogs/VDC/vdcattr/

This behavior is seen in the new VDC emulation I am working on using the new model based on all the results of the tests I've been posting.

Last Edit: Oct 7, 2018 10:18:51 GMT by willymanilly

willymanilly
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Posts: 219

VDC horizontal display greater than 82. Oct 7, 2018 10:42:31 GMT

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Post by willymanilly on Oct 7, 2018 10:42:31 GMT

Oct 7, 2018 9:53:59 GMT tokra said:

I remember hydrophilic had an idea back in the old-forum-days, but sadly those posts are gone.

I can't remember where I copied this from but it could be from the post you are talking about. This information gave me a hint to what to look for when testing.

Attachments:

vdc.txt (7.45 KB)

Commodore 128

VDC horizontal display greater than 82.

Post by willymanilly on Oct 6, 2018 0:34:01 GMT

Post by bjonte on Oct 6, 2018 4:31:44 GMT

Post by bjonte on Oct 6, 2018 7:37:19 GMT

Post by remark on Oct 6, 2018 11:44:09 GMT

Post by willymanilly on Oct 6, 2018 14:23:01 GMT

Post by tokra on Oct 6, 2018 16:09:16 GMT

Post by willymanilly on Oct 7, 2018 1:10:29 GMT

Post by tokra on Oct 7, 2018 9:53:59 GMT

Post by willymanilly on Oct 7, 2018 10:14:51 GMT

Post by willymanilly on Oct 7, 2018 10:42:31 GMT

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